16 might break it.. 四四 makes no sense as 十十 makes no sense... you'd write 百 (100) instead.
And you get the same problem each time you go higher.
You'd need base 4 equivalents of 100 = 百, 1,000 = 千, 10,000 = 万, 100,000,000 = 億,.
Hmm, on the other hand you can have 十万 (100,000), so why not 四四 (16)? What's 20, though...
We've been living out of backpacks on the road for the last ten years, so it's easy to keep track of your stuff... Only item in our bags that hasn't changed is a zip-up flannel towel. It's perfect for keeping your toiletries in order, light-weight and washable, doubles as a flannel on the rare occasions you need such a thing, and has Hello Kitty on it.
Since the bags themselves have been replaced, it's the clear winner. 2nd place is a Tony the Tiger colour-changing spoon from a bag of Frosties in 2016.